1. Field of the Invention
The present invention is directed generally to a power factor correction circuit and specifically to a paper shredder motor power factor correction circuit for use in a paper shredder.
2. Description of the Prior Art
During the use of a paper shredder or a similar type of machine, it is quite common to experience a jam caused by an excessive number of pieces of paper being inserted into the machine. In this situation, to remove the material causing the jam, it is necessary to stop and reverse the shredder. In prior art systems, the operator intercedes when the jam occurs and shuts off power to the machine. The operator may then manually actuate the machine for reverse operation. Alternatively, it has been known to provide a current overload detector, such as circuit breakers of various types which are automatically triggered when an overload occurs in the motor. The operator then resets the circuit breaker and reverses the machine.
With the prior art systems, manual operator intervention is required. Additionally, a sophisticated current sensing system can be quite costly. Furthermore, circuit breakers which may rely on heating of a bi-metal element or the like, may have associated delays. During such a delay, the machine could be damaged.
Further, U.S. Pat. No. 4,495,456 relates to an automatic reverse system for a shredder which automatically causes reversal of the motor when the system becomes jammed. The invention provides for automatic reverse operation without operator intervention. However, the reference does not provide for immediate adjustment of the supply voltage for optimum performance.
A problem related to motors (especially shredder motors) is the changing of the load on the motor caused by different amounts of paper being shredded. The different loads cause operating problems with the motor. A permanent split capacitor motor under full load will run at peak efficiency with a high power factor. However, at no load or partial load, the power factor will drop significantly which results in wasted energy and an overheating of the motor. This condition can be corrected by lowering the voltage to the motor when the motor is partially loaded. As stated above, a paper jam in a shredder causes a great load on the motor used therein. Also, the number of sheets being shredded in a shredder at a particular time is directly proportional to the amount of load on the motor of the shredder.
Although a motor with greater torque may be used to supply sufficient power, it will still overheat under continuous duty. As a result, a shredder motor capable of continuous duty without overheating is needed. The voltage would need to be decreased under no load or reduced load conditions yet be capable of immediately supplying increased voltage with an increased load.